Steps to reproduce the issue

• Have a multilingual site for which the default language code (e.g. en-UK) is hidden and a secondary language (e.g.: it-IT)
• have two valid URLs, one for the primray, one for the secondary language (e.g.: http://nuovaicona.org/exhibitions-and-events/other-venues/luna-d-acqua and http://nuovaicona.org/it/mostre-ed-eventi/altre-sedi/luna-d-acqua) The two URLs are associated, but that doesn't matter much.
• Assuming you already are "in the primary language" visit the first URL
• Now switch language to the secondary one using the language switcher
• Paste the primary language URL in the address bar of your browser

Expected result

The page should be displayed

Actual result

You get a 404

System information (as much as possible)

PHP Built On: Windows NT SMZ 6.3 build 9200 (Windows 8.1 Business Edition) i586
Database Version: 5.6.23
Database Collation: utf8_general_ci
PHP Version: 5.4.39
Web Server: Apache
WebServer to PHP Interface: apache2handler
Joomla! Version: Joomla! 3.4.1 Stable [ Ember ] 21-March-2015 20:30 GMT
Joomla! Platform Version: Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:37.0) Gecko/20100101 Firefox/37.0

Additional comments

This bug creates huge issues when you are set in a secondary language, get an URL for the primary language from another source (e.g.: Google Search) and click on it. Instead of being routed to the correct page you get a 404.

No problems if the "Remove URL Language Code" options is not set in "Language filter".